I live in Texas and here the only things that an employer would be LEGALLY able to divulge is the date of hire/date left company, pay (with your permission ONLY) and "eligible for rehire".
Unfortunately there is nothing you can do about the "eligible for rehire" portion except go to HR and ensure that they are protecting your rights as an employee. You are not hurting anyone by going to HR, as you are leaving the organization anyway and it is probably best that their HR group are aware that their management is doing this.
If they were to give you a "bad recommendation", they would be breaking the law and would be subject to civil suit for defamation. The problem here is trying to prove it. It is not likely that a prospective employer would tell you that you received a bad recommendation and even if they did, you would likely need this information in writing.
I would have to recommend either going to your HR department, stay longer or put in your two weeks' notice and leave. On subsequent applications, state on your "reason for leaving" the information that when you gave notice you were threatened with penalties if you would not extend your employment.
Good luck!